This invention relates to methods of making pins which are used in joints at locations of high wear, heavy abrasion, little or no lubrication and extremely heavy loading.
Large earth moving equipment, such as drag line buckets, have joints with metal to metal contact between a bushing and a pin. Rigging and other machinery have such joints with rotational or sliding loads with extremely high wear. Pins of high strength alloy steel are typically used in these joints.
These pins are extremely large, up to 14" in diameter, and consequently, they are expensive. One common use of this equipment is in coal mining where the presently used pins typically have a wear life of 6-8 days. Maintenance including replacement of the pins brings about down time for very high cost equipment. This down time is very expensive.
Austenitic manganese steel is known for its good wear properties. U.S. Pat. No. 3,048,505 -Doepken, describes examples of austenitic manganese steel. Austenitic manganese steel is also well known for being difficult to work. For this reason, it has not been extensively used. Austenitic manganese steel bushings have been used in joints in the large equipment previously described.
Typically, in such applications, an austenitic manganese steel bushing may wear 3/16 of a inch in the time that a 10" diameter alloy steel pin is reduced to 7" in diameter by wear, and must be replaced. This has been accepted practice, because pins are much easier to replace than bushings, but the frequent replacement of pins remains a serious problem.
Attempts to use cast austenitic manganese steel in large diameter pins have not proven successful. For many reasons, large pins, over 6" diameter, cannot be fabricated entirely from austenitic manganese steel. The low strength characteristics as well as difficulty of working, preclude the use of such pins made entirely of austenitic manganese steel.
Prior attempts to place a shroud of manganese steel on the pin have also not been successful. The reason is that in the applications of use, the pin retainers, or keepers, exert a large axial stress on the pins. In prior pins with manganese shrouds, this has resulted in splitting of the shroud after short periods of use.
It is an object of the present invention to make a pin for heavy duty joints in large equipment, which pin has improved wear characteristics.
It is another object of the present invention to make such a pin with an austenitic manganese shroud which has improved wear characteristics, but is not subject to splitting caused by axial stress.